Endogenous and nitrovasodilator-induced release of NO in the airways of end-stage cystic fibrosis patients

To the Editors: blood pressure changes recorded, as described previously [8] and in the online supplementary material. A variety of isoforms of nitric oxide (NO) synthases are constitutively expressed in human airway and vascular Nearly undetectable levels of NO were found in CF patients endothelial cells continuously generating NO. NO plays an representing an output of 7.6¡6 ppb over 30 s. This is in important role in regulating lung function in health and contrast to patients presented for routine open heart surgery disease including modulation of pulmonary vascular resis- (91.4¡21 ppb over 30 s; fig. 1). Representative traces are tance, airway calibre and host defence. Production of NO and shown in figure 1A and C of the online supplementary its consumption by fluid-phase reactions can be detected and material. monitored in the exhaled air, providing an important window There was a significant increase in gas-phase NO above baseline to assess the dynamics of NO metabolism in health and levels by 250 mg GTN boluses in CF patients (36.7¡6ppb), inflammatory lung conditions, asthma in particular [1]. which was comparable to that seen in control patients with A series of milestone studies uncovered a relative deficiency of routine open heart surgery (48.7¡4 ppb; fig. 1). Representative pulmonary NO availability in cystic fibrosis (CF), a severe traces of GTN-induced exhaled NO are presented in figure 1B chronic inflammatory lung disease with studies generally and D of the online supplementary material. showing reduced exhaled NO [2, 3]. However, there remains These findings provide novel insights into the current debate controversy regarding the anatomical localisation and mechan- on NO exchange dynamics in adult CF. Despite the chronic isms of NO deficiency, and its relationship with CF disease inflammatory nature of the disease, exhaled NO has been progression. By using extended exhaled NO analysis at reported unchanged or low depending on severity of the different expiratory flow rates, indirect studies have attempted disease [2, 4–7]. Our study investigating exhaled NO in to distinguish NO production into bronchial and alveolar ventilated patients undergoing lung transplantation clearly compartments based on basic models [4–7]. However, the fate demonstrates a profound reduction in endogenous gas-phase of NO delivered directly to the alveoli has not been demon- NO in the isolated lower airways of patients with end-stage strated in these patients. We aimed to investigate these issues CF. This conclusion must take into consideration both by evaluating endogenous exhaled NO in end-stage CF in methodological issues regarding tidal measurements of intubated patients undergoing lung transplantation and the exhaled NO and the potential influence of high endogenous dynamism of exhaled NO production from pulmonary micro- carbon dioxide (CO ) on exhaled NO. However, the same vascular metabolism of intravenous nitroglycerin (GTN) [8]. 2 methodology was used for our control population and during Breath-to-breath tidal measurements of NO concentrations in the GTN experiments in the CF patients. Regarding CO2,we the lower airways were performed using a real-time, computer- have not seen major effects of varying endogenous CO2 controlled and integrated system (Logan Research Ltd 2000 and between 3–6% (unpublished observations) but the potential 3000 series, Rochester, UK), as described previously [8[ and in effects of even higher end tidal CO2 in the CF patients cannot detail in the online supplementary material. be excluded. Unpublished observations with end-stage pul- monary hypertension demonstrating better-preserved exhaled To investigate gas-phase NO concentrations in the lower NO also suggest that the reduced endogenous exhaled NO in airways of patients with end-stage CF, seven patients (mean CF may be unique, and is unlikely to be the result of end-stage age, 26 yrs; five males and two females) presented for lung lung disease per se. transplantation were studied after induction of general anaesthetic with endotracheal intubation and mechanical The exact mechanisms of relative NO deficiency in CF are not ventilation. CF patients were contrasted to patients undergoing known. Recent studies utilising extended NO exchange routine open heart surgery for coronary artery bypass grafting analysis resulted in contradictory findings showing no altera- (CABG; n54) exhibiting normal lung function as judged by tions, increased or decreased bronchial fluxes and/or alveolar preoperative respiratory function testing and evaluation of NO concentrations in CF children and adults [4–7]. The routine chest radiography (mean age 56 yrs). The studies were emerging consensus suggests that the main mechanism of approved by the hospital ethics committee and patients NO deficiency in adult CF may relate to increased bronchial provided written consent. inflammation and associated defective NO synthase expres- sion, activity and NO production or increased degradation of Baseline measurements to evaluate endogenous production produced NO [2, 3, 6, 9]. The latter may involve bacterial and release of NO to the gas phase were performed after mechanisms, catalytic and chemical consumption by fluid induction of anaesthetic, prior to excision of the lungs for phase reactions, and during passage through the highly transplant patients, and prior to cardiopulmonary bypass in viscous mucous layer [6, 9]. CABG patients. This was followed in haemodynamically- stable patients with administration of a 250-mg bolus of GTN Our study expands current understanding of alveolar NO into the central venous catheter with exhaled NO and arterial exchange mechanisms by investigating NO fluxes arising from

682 VOLUME 36 NUMBER 3 EUROPEAN RESPIRATORY JOURNAL a) 125 mucosal consumption hypothesis for the dysregulated NO pathways in CF. Furthermore, they also suggest that the CF airways may be therapeutically targeted for exposure by NO 100

-1 through pulmonary metabolism of nitrovasodilators.

" " " 75 T. Varga*,#, T. Kovesi+, J. Gal and N. Marczin*,#, *Section of Anaesthetics, Pain Medicine and Intensive Care, 50 Dept of Surgery and Cancer, Faculty of Medicine, Imperial College London, London, #Royal Brompton and Harefield NHS

Exhaled NO ppb·30 s Foundation Trust, Harefield Hospital, Harefield, Middlesex, 25 " UK, Dept of Anaesthesiology and Intensive Therapy, Faculty of Medicine, Semmelweis University, Budapest, and +Dept of 0 Anaesthesiology and Intensive Therapy, Faculty of Medicine, b) 9 Pecs University, Pecs, Hungary. 8 Correspondence: N. Marczin, Dept of Anaesthetics, Harefield 7 Hospital, Harefield, Middlesex, UK, UB9 6JH. E-mail: n.marczin@ 6 imperial.ac.uk 5 Statement of Interest: None declared 4

3 REFERENCES Peak exhaled NO ppb 2 1 Kharitonov SA, Barnes PJ. Exhaled biomarkers. Chest 2006; 130: 1 1541–1546. 2 Grasemann H, Michler E, Wallot M, et al. Decreased concentration 0 of exhaled nitric oxide (NO) in patients with cystic fibrosis. Pediatr Baseline GTN Pulmonol 1997; 24: 173–177. 3 Kelley TJ, Drumm ML. Inducible nitric oxide synthase expression FIGURE 1. a) Area under curve over 30 s and b) peak exhaled nitric oxide is reduced in cystic fibrosis murine and human airway epithelial (NO) of endogenous gas-phase NO (baseline NO) and exhaled NO in response to cells. J Clin Invest 1998; 102: 1200–1207. intravenous administration of 250-mg bolus of nitroglycerin (GTN) in control patients 4 Shin HW, Rose-Gottron CM, Sufi RS, et al. Flow-independent nitric presenting for open heart surgery for coronary arterial bypass grafting or for lung oxide exchange parameters in cystic fibrosis. Am J Respir Crit Care transplantation and for end-stage cystic fibrosis. GTN values represent changes Med 2002; 165: 349–357. over baseline. 5 Suri R, Paraskakis E, Bush A. Alveolar, but not bronchial nitric oxide production is elevated in cystic fibrosis. Pediatr Pulmonol pulmonary microvascular metabolism of exogenous nitrogly- 2007; 42: 1215–1221. cerin. Our in vivo studies in patients appear to confirm the ex 6 Hofer M, Mueller L, Rechsteiner T, et al. Extended nitric oxide vivo observations of HENNO et al. [10] regarding preserved measurements in exhaled air of cystic fibrosis and healthy adults. endothelium independent vasodilation by nitroprusside in Lung 2009; 187: 307–313. 7 isolated vascular rings of CF pulmonary arteries. Our Hubert D, Aubourg F, Fauroux B, et al. Exhaled nitric oxide in cystic fibrosis: relationships with airway and lung vascular preliminary results extend these studies to the microvascula- impairments. Eur Respir J 2009; 34: 117–124. ture and airway compartments by suggesting a notably 8 Marczin N, Riedel B, Royston D, et al. Intravenous nitrate preserved ability of the end-stage CF lung microvasculature vasodilators and exhaled nitric oxide. Lancet 1997; 349: 1742. to convert GTN and release NO into the alveoli and airways 9 Grasemann H, Lax H, Treseler JW, et al. Dornase alpha and without evidence of increased consumption either in the exhaled NO in cystic fibrosis. Pediatr Pulmonol 2004; 38: 379–385. alveolar fluid or gas phase. This is remarkable in relation to 10 Henno P, Maurey C, Danel C, et al. Pulmonary vascular both the profound reduction in endogenous NO release and dysfunction in end-stage cystic fibrosis: role of NF-kB and the potential for pulmonary vascular dysfunction associated endothelin-1. Eur Respir J 2009; 34: 1329–1337. with end-stage CF in some patients [7, 10]. Altogether, these data lend strong support for the bronchial epithelial and DOI: 10.1183/09031936.00025610

c

EUROPEAN RESPIRATORY JOURNAL VOLUME 36 NUMBER 3 683